Unilateral pneumonectomy in laboratory animals induces a stimulus to the growth of the remaining lung such that lung volume greatly increases above normal. It is proposed to locate the sites at which new growth occurs and compare newly formed tissue with preexisting "mature" tissue. The main thrust of the research is to ascertain the effects of air pollutant gases on this accelerated lung development and to determine whether growth is impaired on exposure to pollutants in concentrations found in urban environments. The characterization of this "stimulated" lung growth and development in control and in animals exposed to ozone, and other oxidants, will derive from measurements of pulmonary function, from quantitative morphometry and light and electron microscopy and from biochemical analyses. The experimental design offers the advantage of investigating the effects of environmental stress on a compromised organ that consists of both mature tissue and tissue in a state of development. In this respect, the findings may have particular significance in the areas of neo-natal development and pneumonectomy in the human.